This invention relates to spin coating of PCMO thin films, and specifically to an annealing process to enhance the bipolar switching properties of PCMO thin films in RRAM applications.
Electrically programmable resistance non volatile memory device operated at room temperature that use spin on PCMO thin film on Pt substrate was demonstrated by Zhuang, et al., in U.S. patent application Ser. No. 10/256,380, filed Sep. 26, 2002, for Method Resistance Memory Metal Oxide Thin Film Deposition, describes a technique for forming a CMR layer in a RAM device. The PCMO thin film was grown on a Platinum layer, and, following a low heat treatment, exhibited amorphous or polycrystalline structure. This resistor may be reversibly programmed to a high or a low resistance state by unipolar electrical pulses having different pulse widths. However, in order to use the CMR in a RRAM application, bipolar electrical pulses switching properties are more preferred. These switching properties require a well-crystallized PCMO thin film.
A method of forming a PCMO thin film in a RRAM device includes preparing a substrate; depositing a metal barrier layer on the substrate; forming a bottom electrode on the barrier layer; spin-coating a layer of Pr1xe2x88x92xCaxMnO3 (PCMO) on the bottom electrode using a PCMO precursor consisting of Pr(CH3CO2)3.H2O, Ca(CH3CO2)2.H2O, and Mn(III)(CH3CO2)3.2H2O, in an acetic acid solvent; baking the PCMO thin film in at least one or more separate baking steps, wherein the baking steps may include, e.g., a first baking step at a temperature of between about 50xc2x0 C. to 150xc2x0 C. for between about ten seconds to one hour; a second baking step at a temperature of between about 100xc2x0 C. to 200xc2x0 C. for between about ten seconds to one hour; and a third baking step at a temperature of between about 150xc2x0 C. to 300xc2x0 C. for between about ten seconds to one hour. Alternately, a single baking step at a temperature of between about 50xc2x0 C. to 300xc2x0 C. for between about ten seconds to one hour may be used. The baking step(s) are followed by annealing the PCMO thin film in a first annealing step at a temperature of between about 400xc2x0 C. to 900xc2x0 C. for between about ten seconds to one hour after each spin-coating step; repeating the spin-coating step, the baking step and the first annealing step until the PCMO thin film has a desired thickness; annealing the PCMO thin film in a second annealing step at a temperature of between about 450xc2x0 C. to 1000xc2x0 C., for between about one minute to twenty-four hours, thereby producing a PCMO thin film having a crystalline structure of Pr1xe2x88x92xCaxMnO3, where 0.2 less than =X less than =0.5; depositing a top electrode; patterning the top electrode; and completing the RRAM device.
It is an object of the invention to specify a high temperature annealing method of a spin-coated PCMO thin film to form a well-crystallized PCMO thin film having bipolar electrical pulse switching properties for use in RRAM applications.
This summary and objectives of the invention are provided to enable quick comprehension of the nature of the invention. A more thorough understanding of the invention may be obtained by reference to the following detailed description of the preferred embodiment of the invention in connection with the drawings.